Conclusions
Pollen morphology of Quercus pollen in the United States is
rarely studied. Sizes between Quercus pollen of 3 oak sections,
of 5 phylogenetic groups, and of 23 species were applied LM and SEM
morphological measurements to investigate classification and
differentiation between phylogenetic lineages of Quercus native
to California.
Jarvis et al.’s (1992) study of oak morphology suggests that both polar
axis and equatorial diameter of evergreen oak pollen are smaller than
that of deciduous oak pollen in southwestern Sichuan Province,
China . The observation was not found in this study. Even so, deciduous
oak pollen tends to perform shorter furrows than evergreen oak pollen
does. New World Quercus section, Protobalanus , has the
smallest average size and variation in three studied sections. This
group is unique by its smooth pollen surface and uniformed dense
scabratae. The higher similarity of sizes between Quercus and Lobatae sections coincide with the closer phylogenetic distance
of these two sections than them and Protobalanus . Pollen grains
of studied species in Quercus and Lobatae sections were
classified into “(micro) verrucate” type, while that in Protobalanus was classified into “rodlike masked” type. We
manually separated the ultrastructure features into 3 types. Type 1 and
type 2 can be matched to (micro) verrucate category in Denk’s and
Grimm’s classification (Denk and Grimm, 2009). Type 2 pollen grains have
ultraelements on each “(micro) verrucate” elements which type 1 pollen
grains do not have. Type 3 can be matched to rodlike masked category. The length of polar view character shows phylogenetic signal in 20 Quercus species. The distance between 2 furrows in Lobatae sections, Q. agrifolia, Q. kelloggii, Q. parvula, and Q. wislizeni, also has phylogenetic signal. Further investigations will be focused on details of surface ultrastructure and trait-environment relationships.